Can't get camshaft bolt off

I'm having a lot of trouble getting my camshaft bolt off. I'm wondering if I'm doing something wrong. This is the bolt in question.

http://i.imgur.com/rI30lSX.jpg

From my understanding reading the FSM and other sources, most people use a wrench to hold the camshaft steady and then put a 19mm wrench on the camshaft bolt itself. I'm pretty sure to turn the bolt counter-clockwise, I'm supposed to start from near the top and then push downwards. When I do this, however, it starts to round the bolt a bit or the camshaft itself starts turning. I just want to make sure I'm doing this right (because I can't afford to round the bolt anymore or I'll be in even bigger doo-doo). Am I doing anything wrong? Any tips on how to get that bolt off?

I've found that these can be tight too. One of my posts has a picture of how I did it.
You mention a wrench. I use a 19mm 1/2" drive six-point socket with a breaker bar, and remove the half-round plug in the end of the head to allow access this way. On the camshaft I use a 10" Crescent wrench on the rough hex at the center of the camshaft, and support the end with a 2x4 against the floor. That's with the engine on a stand, though. I see that your engine is still in the van so the crescent wrench can be supported against the body work to keep it from turning.
I hope there's enough meat on the bolt for a six-point socket to get a good purchase on it. Otherwise things get much uglier.

Thanks so much! Getting the half-moon plug off to allow more access is exactly what I needed to get a 19mm socket on that bolt. That made all the difference. :dance2:

I'll be getting a new camshaft sprocket bolt to replace the one that I rounded. I did a little researching, and for anyone that needs it in the future, the part number is 90105-12261.

Now, I've got a different problem, but I'll create a different thread for that :)